1. Field of the Invention
The present invention relates to a radio-frequency device and wireless communication device, and more particularly, to a radio-frequency device and wireless communication device capable of enhancing antenna isolation so as to dispose multiple antennas in a limited space while maintaining preferable antenna efficiency and bandwidth.
2. Description of the Prior Art
Electronic products with wireless communication functionalities, such as laptops, tablet PCs, personal digital assistants (PDAs), mobile phones, wireless base stations, smart meters, and USB dongles, utilize antennas to send and receive wireless signals so as to access wireless networks. In order to let the users access wireless communication networks more conveniently, the antenna bandwidth should be as broad as possible so that more communication protocols can be complied with, while the antenna size should be minimized to meet a demand for smaller and lighter products. In addition, with evolution of wireless communication technologies a wireless communication device may be required to equip more antennas. For example, a modern USB dongle may be equipped with multiple sets of antennas to establish a plurality of antenna channels for spatial diversity and provide multiple antenna patterns, which allows the user to execute different applications using different wireless communication systems (e.g. Bluetooth and Wi-Fi) on the same frequency band at the same time. Furthermore, the spectrum efficiency and the transmission speed may be enhanced with multiple sets of antennas, thereby improving the communication quality. Since multiple sets of antennas are disposed in a communication device, the interference problems have become one of the important design considerations for antenna designs.
In general, multiple sets of antennas are respectively disposed on the diagonal positions or are kept in the farthest distance between one another on the longest edge of a wireless communication device so as to minimize the interference between antennas and achieve better complementary antenna characteristics. However, if the overall size of the wireless communication device or the available space for disposing the antennas is very small, careful considerations must be taken when drawing the layout of the antennas.
In addition, the broadband requirement has become a primary item for antenna designs as the evolution of wireless communication technologies. The common broadband antennas, such as planar inverted-F antennas, can meet the requirement of multi-frequency operation; however, the radiation elements of such antennas are too long to be installed in a miniature wireless communication system. Furthermore, the low frequency band of these kinds of antennas is too narrow (only about 110 MHz) so that they cannot meet the broadband requirement of the wireless communication systems.
Therefore, how to design multiple sets of antennas in a limited space which meets all of the antenna requirements for transmission, bandwidth, efficiency, and isolation is an important topic to be addressed and discussed.